Based on the results of morphological studies of materials on bitterlings (genus Rhodeus) and loaches (genus Misgurnus) collected in the Ili River basin (Kazakhstan) in 2011, it is shown for the first time that the rosy bitterling R. ocellatus and Nikolsky’s loach M. nikolskyi have naturalized in the Balkhash–Ili basin.

The diversity and distribution of fish in the water bodies of the Black Irtysh basin was studied in connection with six abiotic environmental parameters (surface flow velocity, width and depth of rivers, connection with the main river, and bottom and maximum temperature). The current species diversity of fish consists of 29 native and 11 alien species. The diversity of right and left tributaries varies greatly as a result of differences in abiotic parameters. The presence of a hydrological connection of reservoirs by itself does not guarantee the distribution of species throughout the basin. Rare indigenous Siberian Taimen Hucho taimen and Markakol Lenok Brachymystax savinovi were regularly found in the right tributaries of the Irtysh River and Lake Markakol, respectively. New fish species to the Kazakh section of the Black Irtysh River have been discovered: Tibetan stone loach Triplophysa stolickai, Severtsov’s loach Triplophysa sewerzowi and alien fish species as asp Leuciscus aspius, Chinese false gudgeon Abbottina rivularis, sunbleak Leucaspius delinetaus, and Misgurnus sp.